The uncertainty in the dose calibration of high-energy radiation therapy accelerators using calibrated ionization chambers is on the order of plus or minus 5%. Many of the problems associated with ionization chambers do not exist for the Fricke ferrous sulfate dosimeter, however, the chemical yields, G values, for the Fricke dosimeter have similar uncertainties. It is proposed to determine the G values for the Fricke dosimeter for X-rays and electrons in the energy range of 1-60 MeV. The response of the Fricke dosimeter will be compared to that of absorbed-dose calorimeters to be constructed from graphite and water. The graphite calorimeter will be identical to the one in routine use at the National Bureau of Standards. The water calorimeter is a new device which is currently being evaluated at the NBS, our laboratory, and several other research institutions. By comparing the two calorimeters, the method of transferring the dose-to-graphite to the dose-to-Fricke dosimeter (water) may be tested for accuracy and refined. This procedure will reduce the uncertainty in measured G-values to the accuracy attainable with the Fricke dosimeter.